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<\/figure>\n\n\n\nWhat Is Laser-Induced Damage Threshold?<\/h2>\n\n\n\n
Laser-induced damage threshold describes the laser exposure level at which permanent damage is detected on or within an optical component.<\/p>\n\n\n\n
Damage may appear as:<\/p>\n\n\n\n
- \n
- Surface pits<\/li>\n\n\n\n
- Microscheurtjes<\/li>\n\n\n\n
- Local melting<\/li>\n\n\n\n
- Coating delamination<\/li>\n\n\n\n
- Coating discoloration<\/li>\n\n\n\n
- Verhoogde verstrooiing<\/li>\n\n\n\n
- Bulk modification<\/li>\n\n\n\n
- Internal fractures<\/li>\n\n\n\n
- Transmission loss<\/li>\n\n\n\n
- Catastrophic cracking<\/li>\n<\/ul>\n\n\n\n
ISO 21254-1:2025 defines terminology and general principles for determining LIDT and for assuring the laser-radiation handling capability of optical components. It replaced the earlier 2011 edition of Part 1.<\/p>\n\n\n\n
LIDT is not a universal material constant in the same way as density or melting temperature.<\/p>\n\n\n\n
A sapphire window does not have one single threshold that applies to every laser. The reported threshold belongs to a particular component, manufacturing condition and test configuration.<\/p>\n\n\n\n
Why Buyers Should Not Ask Only for \u201cthe Sapphire LIDT\u201d<\/h2>\n\n\n\n
A request such as the following is incomplete:<\/p>\n\n\n\n
\n
What is the LIDT of your sapphire window?<\/p>\n<\/blockquote>\n\n\n\n
The supplier cannot provide a technically reliable answer without knowing the laser conditions.<\/p>\n\n\n\n
A more useful request would state:<\/p>\n\n\n\n
\n
Please provide the LIDT of the finished AR-coated sapphire window at 1064 nm using 10 ns pulses, the specified beam diameter, repetition rate and pulse-on-site test method.<\/p>\n<\/blockquote>\n\n\n\n
The difference is important because published research comparing optical materials, including sapphire, has shown substantial changes in damage or ablation threshold when pulse duration changes from nanoseconds to picoseconds or femtoseconds. These results should not be treated as interchangeable values for a commercial finished optic, but they demonstrate why pulse duration must always accompany a threshold number.<\/p>\n\n\n\n
LIDT Units for Pulsed and Continuous-Wave Lasers<\/h2>\n\n\n\n
Pulsed Lasers<\/h3>\n\n\n\n
For pulsed lasers, LIDT is commonly reported as energy fluence, often in:<\/p>\n\n\n\n
- \n
- J\/cm\u00b2<\/li>\n\n\n\n
- mJ\/cm\u00b2<\/li>\n<\/ul>\n\n\n\n
Fluence describes laser energy distributed over an illuminated area.<\/p>\n\n\n\n
For a simplified uniform beam:<\/p>\n\n\n\n
Fluence = pulse energy \u00f7 illuminated area<\/strong><\/p>\n\n\n\n
Real laser beams are often Gaussian rather than uniform. The peak fluence at the beam center can therefore be significantly higher than the average energy divided by the nominal beam area.<\/p>\n\n\n\n
A valid test report should identify:<\/p>\n\n\n\n
- \n
- Balkprofiel<\/li>\n\n\n\n
- Beam-radius definition<\/li>\n\n\n\n
- Effective beam area<\/li>\n\n\n\n
- Whether the reported value is peak or average fluence<\/li>\n\n\n\n
- Method used to calculate fluence<\/li>\n<\/ul>\n\n\n\n
Continuous-Wave Lasers<\/h3>\n\n\n\n
For continuous-wave and long-pulse systems, damage may be driven more strongly by absorption and thermal accumulation.<\/p>\n\n\n\n
Results may be expressed using:<\/p>\n\n\n\n
- \n
- W\/cm\u00b2<\/li>\n\n\n\n
- kW\/cm\u00b2<\/li>\n\n\n\n
- Incident laser power<\/li>\n\n\n\n
- Absorbed power<\/li>\n\n\n\n
- Time to damage<\/li>\n<\/ul>\n\n\n\n
A CW result cannot be directly compared with a nanosecond or femtosecond pulsed-laser result.<\/p>\n\n\n\n
For CW applications, the buyer should also consider:<\/p>\n\n\n\n
- \n
- Coating absorption<\/li>\n\n\n\n
- Substrate absorption<\/li>\n\n\n\n
- Beam dwell time<\/li>\n\n\n\n
- Cooling conditions<\/li>\n\n\n\n
- Montagemethode<\/li>\n\n\n\n
- Edge contact<\/li>\n\n\n\n
- Thermal gradients<\/li>\n\n\n\n
- Environmental temperature<\/li>\n<\/ul>\n\n\n\n
The Most Important Parameters Affecting Sapphire Window LIDT<\/h2>\n\n\n\n
1. Laser Wavelength<\/h2>\n\n\n\n
The operating wavelength affects how the sapphire substrate, surface contamination and optical coating interact with the laser.<\/p>\n\n\n\n
In de offerteaanvraag moet het volgende worden vermeld:<\/p>\n\n\n\n
- \n
- Nominal wavelength<\/li>\n\n\n\n
- Wavelength tolerance<\/li>\n\n\n\n
- Single wavelength or broadband operation<\/li>\n\n\n\n
- Fundamental or harmonic wavelength<\/li>\n\n\n\n
- Presence of residual pump wavelengths<\/li>\n\n\n\n
- Possible amplified spontaneous emission<\/li>\n\n\n\n
- Multiple wavelengths passing through the window<\/li>\n<\/ul>\n\n\n\n
Examples may include:<\/p>\n\n\n\n
- \n
- 355 nm<\/li>\n\n\n\n
- 532 nm<\/li>\n\n\n\n
- 1030 nm<\/li>\n\n\n\n
- 1064 nm<\/li>\n\n\n\n
- 1550 nm<\/li>\n\n\n\n
- 2940 nm<\/li>\n<\/ul>\n\n\n\n
An LIDT test performed at 1064 nm does not automatically qualify the same optic for 355 nm.<\/p>\n\n\n\n
At shorter wavelengths, small defects, contaminants and coating absorption may behave differently. The coating material system and electric-field distribution inside the coating will also change with wavelength.<\/p>\n\n\n\n
2. Pulse Duration<\/h2>\n\n\n\n
Pulse duration is one of the most important items in an LIDT specification.<\/p>\n\n\n\n
Common laser regimes include:<\/p>\n\n\n\n
- \n
- Millisecond<\/li>\n\n\n\n
- Microsecond<\/li>\n\n\n\n
- Nanosecond<\/li>\n\n\n\n
- Picosecond<\/li>\n\n\n\n
- Femtosecond<\/li>\n<\/ul>\n\n\n\n
Longer pulses allow more time for absorbed energy to produce thermal effects. Ultrashort pulses can cause damage through strong nonlinear ionization and rapid energy deposition before heat diffuses far from the interaction region.<\/p>\n\n\n\n
Research on sapphire and other transparent optical materials shows that threshold behavior changes substantially across femtosecond, picosecond and nanosecond regimes. A study comparing sapphire with several glass materials found major differences between the measured single-pulse ablation thresholds at approximately 1030\u20131064 nm as pulse duration changed.<\/p>\n\n\n\n
Never convert an LIDT value from one pulse duration to another using a generic scaling rule unless the relationship has been validated for the specific substrate, surface, coating and test range.<\/p>\n\n\n\n
3. Pulse Energy<\/h2>\n\n\n\n
Pulse energy determines the total energy delivered during each laser pulse.<\/p>\n\n\n\n
However, pulse energy alone is not sufficient for optical-window selection.<\/p>\n\n\n\n
The same pulse energy can create very different fluence levels depending on whether it is distributed over:<\/p>\n\n\n\n
- \n
- A 10 mm beam<\/li>\n\n\n\n
- A 2 mm beam<\/li>\n\n\n\n
- A tightly focused spot<\/li>\n\n\n\n
- An elliptical footprint<\/li>\n\n\n\n
- A nonuniform beam containing hot spots<\/li>\n<\/ul>\n\n\n\n
The RFQ should provide both pulse energy and beam dimensions at the sapphire window.<\/p>\n\n\n\n
4. Beam Diameter<\/h2>\n\n\n\n
A supplier must know the actual beam size at the optical surface, not only the beam diameter elsewhere in the laser system.<\/p>\n\n\n\n
Geef het volgende op:<\/p>\n\n\n\n
- \n
- Beam diameter at the window<\/li>\n\n\n\n
- Beam-radius definition<\/li>\n\n\n\n
- Meetmethode<\/li>\n\n\n\n
- Circular or elliptical beam<\/li>\n\n\n\n
- Beam size in both axes<\/li>\n\n\n\n
- Distance from the focus<\/li>\n\n\n\n
- Expected alignment variation<\/li>\n<\/ul>\n\n\n\n
Beam size can influence both the operating fluence and the measured LIDT result. Research on sub-picosecond optical damage testing has specifically examined beam-size effects, reinforcing the need to document beam dimensions when comparing threshold results.<\/p>\n\n\n\n
5. Spatial Beam Profile<\/h2>\n\n\n\n
A nominally Gaussian beam contains a higher intensity near its center than near its edges.<\/p>\n\n\n\n
Other possible profiles include:<\/p>\n\n\n\n
- \n
- Top-hat<\/li>\n\n\n\n
- Multimode<\/li>\n\n\n\n
- Annular<\/li>\n\n\n\n
- Elliptical<\/li>\n\n\n\n
- Irregular<\/li>\n\n\n\n
- Speckled<\/li>\n\n\n\n
- Beam with localized hot spots<\/li>\n<\/ul>\n\n\n\n
Hot spots may cause local damage even when the average fluence appears acceptable.<\/p>\n\n\n\n
The buyer should specify whether the system includes:<\/p>\n\n\n\n
- \n
- Beam homogenization<\/li>\n\n\n\n
- Spatial filtering<\/li>\n\n\n\n
- Mode changes during operation<\/li>\n\n\n\n
- Alignment transients<\/li>\n\n\n\n
- Focus shifts<\/li>\n\n\n\n
- Back reflections<\/li>\n\n\n\n
- Interference patterns<\/li>\n<\/ul>\n\n\n\n
A supplier LIDT report based on a controlled Gaussian test beam may not predict the behavior of an unstable multimode production laser containing strong hot spots.<\/p>\n\n\n\n
6. Pulse Repetition Rate<\/h2>\n\n\n\n
Repetition rate affects the time available for heat to dissipate between pulses.<\/p>\n\n\n\n
Important values include:<\/p>\n\n\n\n
- \n
- Single shot<\/li>\n\n\n\n
- Low-frequency pulsed operation<\/li>\n\n\n\n
- Kilohertz operation<\/li>\n\n\n\n
- Megahertz operation<\/li>\n\n\n\n
- Burst mode<\/li>\n\n\n\n
- Variable-frequency operation<\/li>\n<\/ul>\n\n\n\n
High repetition rates can create thermal accumulation or incubation effects even when the fluence of each individual pulse is below a single-pulse threshold.<\/p>\n\n\n\n
A comparative femtosecond study of several optical coatings found substantially lower measured thresholds at megahertz repetition rates than at kilohertz rates under otherwise similar pulse conditions. Although the result was not specific to a bare sapphire window, it demonstrates why repetition rate must be included when qualifying a finished laser optic.<\/p>\n\n\n\n
7. Number of Pulses per Test Site<\/h2>\n\n\n\n
A single pulse and thousands of pulses at the same position are not equivalent exposure conditions.<\/p>\n\n\n\n
ISO 21254-2:2011 describes both 1-on-1 and S-on-1 threshold tests and remains the relevant published Part 2 while it undergoes review.<\/p>\n\n\n\n
1-on-1 Test<\/h3>\n\n\n\n
In a 1-on-1 test, one pulse is applied to each previously unexposed test site.<\/p>\n\n\n\n
This method is useful for evaluating single-pulse damage behavior.<\/p>\n\n\n\n
S-on-1 Test<\/h3>\n\n\n\n
In an S-on-1 test, a defined number of pulses is applied to each test site.<\/p>\n\n\n\n
This method can better represent systems in which the same area of the sapphire window experiences repeated exposure.<\/p>\n\n\n\n
The report should state:<\/p>\n\n\n\n
- \n
- Pulses per site<\/li>\n\n\n\n
- Pulse frequency<\/li>\n\n\n\n
- Number of test sites<\/li>\n\n\n\n
- Fluence levels<\/li>\n\n\n\n
- Damage probability method<\/li>\n\n\n\n
- Whether the beam was moved between sites<\/li>\n<\/ul>\n\n\n\n
A value reported as \u201c10 J\/cm\u00b2\u201d without the pulse-count method is incomplete.<\/p>\n\n\n\n
8. Angle of Incidence<\/h2>\n\n\n\n
The angle of incidence affects:<\/p>\n\n\n\n
- \n
- Beam footprint<\/li>\n\n\n\n
- Polarization behavior<\/li>\n\n\n\n
- Fresnel reflection<\/li>\n\n\n\n
- Prestaties van de coating<\/li>\n\n\n\n
- Internal electric-field distribution<\/li>\n\n\n\n
- Effective optical path<\/li>\n\n\n\n
- Back-reflection direction<\/li>\n<\/ul>\n\n\n\n
A circular beam becomes elliptical when it strikes the window at an angle. The energy is then distributed across a larger physical area, but the coating may also experience different electric-field conditions than it would at normal incidence.<\/p>\n\n\n\n
The LIDT test should be conducted at the intended angle of incidence whenever the angle is significant to the system.<\/p>\n\n\n\n
9. Polarization<\/h2>\n\n\n\n
The buyer should state whether the laser is:<\/p>\n\n\n\n
- \n
- Unpolarized<\/li>\n\n\n\n
- Randomly polarized<\/li>\n\n\n\n
- Linearly polarized<\/li>\n\n\n\n
- S-polarized<\/li>\n\n\n\n
- P-polarized<\/li>\n\n\n\n
- Circularly polarized<\/li>\n<\/ul>\n\n\n\n
Polarization can affect the reflectance and electric-field distribution of coatings used at nonzero angles of incidence.<\/p>\n\n\n\n
For coated sapphire windows installed at 45\u00b0 or another oblique angle, the supplier may need separate optical and LIDT considerations for S and P polarization.<\/p>\n\n\n\n
10. Sapphire Crystal Orientation<\/h2>\n\n\n\n
Sapphire is a crystalline and optically anisotropic material.<\/p>\n\n\n\n
The window specification may therefore include:<\/p>\n\n\n\n
- \n
- C-vlak<\/li>\n\n\n\n
- A-vlak<\/li>\n\n\n\n
- R-vlak<\/li>\n\n\n\n
- M-vlak<\/li>\n\n\n\n
- Custom orientation<\/li>\n\n\n\n
- Crystal-axis direction relative to polarization<\/li>\n<\/ul>\n\n\n\n
For general protective laser windows, the supplier may recommend an orientation based on manufacturing availability and application conditions.<\/p>\n\n\n\n
For polarization-sensitive, birefringence-sensitive or ultrafast systems, the buyer should evaluate crystal orientation together with:<\/p>\n\n\n\n
- \n
- Propagation direction<\/li>\n\n\n\n
- Polarisatie<\/li>\n\n\n\n
- Dikte<\/li>\n\n\n\n
- Allowed retardance<\/li>\n\n\n\n
- Wavefront requirements<\/li>\n\n\n\n
- Thermal load<\/li>\n<\/ul>\n\n\n\n
The orientation used for the tested sample should match the orientation of the production window when orientation can affect system performance.<\/p>\n\n\n\n
11. Bare Sapphire Versus Coated Sapphire<\/h2>\n\n\n\n
A bare polished sapphire substrate and an AR-coated sapphire window are different laser components.<\/p>\n\n\n\n
The finished coated optic may fail because of:<\/p>\n\n\n\n
- \n
- Coating absorption<\/li>\n\n\n\n
- Layer defects<\/li>\n\n\n\n
- Nodules<\/li>\n\n\n\n
- Pinholes<\/li>\n\n\n\n
- Verontreiniging<\/li>\n\n\n\n
- Poor adhesion<\/li>\n\n\n\n
- High electric-field concentration<\/li>\n\n\n\n
- Coating stress<\/li>\n\n\n\n
- Substrate defects beneath the coating<\/li>\n<\/ul>\n\n\n\n
The coating may become the limiting element even when the sapphire substrate itself could tolerate a higher exposure.<\/p>\n\n\n\n
The buyer should therefore request LIDT data for:<\/p>\n\n\n\n
\n
The finished coating on the specified sapphire substrate.<\/p>\n<\/blockquote>\n\n\n\n
A substrate-only LIDT value should not be presented as the guaranteed LIDT of an AR-coated production window.<\/p>\n\n\n\n
12. Coating Design<\/h2>\n\n\n\n
Two AR coatings with similar transmission can have different laser-damage performance.<\/p>\n\n\n\n
The result may depend on:<\/p>\n\n\n\n
- \n
- Coating materials<\/li>\n\n\n\n
- Layer thicknesses<\/li>\n\n\n\n
- Number of layers<\/li>\n\n\n\n
- Deposition method<\/li>\n\n\n\n
- Absorption<\/li>\n\n\n\n
- Defect density<\/li>\n\n\n\n
- Internal electric-field distribution<\/li>\n\n\n\n
- Post-deposition treatment<\/li>\n\n\n\n
- Cleaning and handling<\/li>\n\n\n\n
- Coating run consistency<\/li>\n<\/ul>\n\n\n\n
A broadband AR coating often requires a more complex layer structure than a narrowband coating. More complex does not automatically mean unsuitable, but the coating should be designed for both spectral performance and the required laser exposure.<\/p>\n\n\n\n
The RFQ should state whether the priority is:<\/p>\n\n\n\n
- \n
- Lowest reflection<\/li>\n\n\n\n
- Broadest bandwidth<\/li>\n\n\n\n
- Highest damage resistance<\/li>\n\n\n\n
- Milieuduurzaamheid<\/li>\n\n\n\n
- A defined compromise among these requirements<\/li>\n<\/ul>\n\n\n\n
13. Surface Quality and Polishing<\/h2>\n\n\n\n
Laser damage frequently begins at a defect rather than in an ideal, defect-free region.<\/p>\n\n\n\n
Potential initiation sites include:<\/p>\n\n\n\n
- \n
- Krassen<\/li>\n\n\n\n
- Vindplaatsen<\/li>\n\n\n\n
- Embedded polishing residue<\/li>\n\n\n\n
- Subsurface grinding damage<\/li>\n\n\n\n
- Edge-chips<\/li>\n\n\n\n
- Contamination particles<\/li>\n\n\n\n
- Coating nodules<\/li>\n\n\n\n
- Localized absorption centers<\/li>\n<\/ul>\n\n\n\n
Research on laser optics has repeatedly shown that polishing conditions, surface preparation and subsurface damage can influence damage resistance. Studies on fused-silica laser optics, for example, have demonstrated improvements after processes that remove or reduce damaged surface layers. The exact numerical improvement cannot be transferred directly to sapphire, but the manufacturing principle remains relevant when qualifying high-power optical surfaces.<\/p>\n\n\n\n
For high-power sapphire windows, the drawing should define measurable requirements rather than simply stating \u201claser quality.\u201d<\/p>\n\n\n\n
Useful specifications may include:<\/p>\n\n\n\n
- \n
- Vereiste inzake kras- en graafwerkzaamheden<\/li>\n\n\n\n
- Oppervlakteruwheid<\/li>\n\n\n\n
- Vlakheid<\/li>\n\n\n\n
- Vrije opening<\/li>\n\n\n\n
- Edge-chip limits<\/li>\n\n\n\n
- Reinigingsmethode<\/li>\n\n\n\n
- Coating-defect criteria<\/li>\n\n\n\n
- Inspection magnification<\/li>\n<\/ul>\n\n\n\n
14. Surface Cleanliness<\/h2>\n\n\n\n
Dust, fingerprints, oils, polishing residue and cleaning stains can absorb or scatter laser energy.<\/p>\n\n\n\n
A qualified sapphire window can be damaged in service if it is handled or cleaned incorrectly after delivery.<\/p>\n\n\n\n
The buyer should define:<\/p>\n\n\n\n
- \n
- Final cleaning process<\/li>\n\n\n\n
- Packaging cleanliness<\/li>\n\n\n\n
- Cleanroom class when required<\/li>\n\n\n\n
- Handling gloves<\/li>\n\n\n\n
- Approved cleaning solvents<\/li>\n\n\n\n
- Allowed wiping materials<\/li>\n\n\n\n
- Inspection before installation<\/li>\n\n\n\n
- Storage conditions<\/li>\n<\/ul>\n\n\n\n
The system design should also minimize later contamination from:<\/p>\n\n\n\n
- \n
- Lubricants<\/li>\n\n\n\n
- Adhesives<\/li>\n\n\n\n
- Elastomers<\/li>\n\n\n\n
- Vacuum outgassing<\/li>\n\n\n\n
- Airborne particles<\/li>\n\n\n\n
- Process deposits<\/li>\n\n\n\n
- Ablation debris<\/li>\n<\/ul>\n\n\n\n
ISO\/TR 20811:2017 discusses laser-induced molecular contamination in relation to laser-induced damage and the ISO 21254 test framework, highlighting the role of molecular contamination on optical surfaces exposed to laser radiation.<\/p>\n\n\n\n
15. Bulk Defects and Internal Quality<\/h2>\n\n\n\n
Although surface and coating damage receive significant attention, damage can also occur inside the sapphire.<\/p>\n\n\n\n
Possible internal concerns include:<\/p>\n\n\n\n
- \n
- Toevoegingen<\/li>\n\n\n\n
- Bubbels<\/li>\n\n\n\n
- Growth-related defects<\/li>\n\n\n\n
- Local impurities<\/li>\n\n\n\n
- Stress<\/li>\n\n\n\n
- Subsurface cracks<\/li>\n\n\n\n
- Internal contamination<\/li>\n\n\n\n
- Local refractive-index variations<\/li>\n<\/ul>\n\n\n\n
Research examining bulk damage in sapphire and Ti over pulse durations from femtoseconds to nanoseconds shows that bulk threshold behavior depends strongly on exposure conditions and material state.<\/p>\n\n\n\n
For demanding systems, the buyer may require:<\/p>\n\n\n\n
- \n
- Materiaalcertificaat<\/li>\n\n\n\n
- Crystal-growth lot<\/li>\n\n\n\n
- Orientation certificate<\/li>\n\n\n\n
- Internal visual inspection<\/li>\n\n\n\n
- Polariscopic inspection<\/li>\n\n\n\n
- Inclusion limits<\/li>\n\n\n\n
- Bulk-scatter inspection<\/li>\n\n\n\n
- Traceerbaarheid van partijen<\/li>\n<\/ul>\n\n\n\n
Surface LIDT Versus Bulk LIDT<\/h2>\n\n\n\n
A supplier should clearly identify where damage was evaluated.<\/p>\n\n\n\n
Entrance-Surface Damage<\/h3>\n\n\n\n
Damage begins on the first optical surface exposed to the beam.<\/p>\n\n\n\n
Possible causes include contamination, coating defects, scratches or high local electric fields.<\/p>\n\n\n\n
Exit-Surface Damage<\/h3>\n\n\n\n
Damage begins on the second surface.<\/p>\n\n\n\n
Exit-surface behavior can differ because the light has already propagated through the substrate and may interact differently with defects or reflections.<\/p>\n\n\n\n
Bulk Damage<\/h3>\n\n\n\n
Damage occurs within the sapphire rather than at a polished surface.<\/p>\n\n\n\n
Edge Damage<\/h3>\n\n\n\n
Damage develops near an edge, bevel or mount.<\/p>\n\n\n\n
This may be related to beam clipping, scattering, contamination, local stress or reflected energy.<\/p>\n\n\n\n
The test report should identify whether the reported value represents:<\/p>\n\n\n\n
- \n
- Entrance surface<\/li>\n\n\n\n
- Exit surface<\/li>\n\n\n\n
- Coating<\/li>\n\n\n\n
- Uncoated substrate<\/li>\n\n\n\n
- Bulk material<\/li>\n\n\n\n
- Complete finished component<\/li>\n<\/ul>\n\n\n\n
Damage Threshold Is Statistical<\/h2>\n\n\n\n
Laser-induced damage does not always occur at exactly the same fluence on every test site.<\/p>\n\n\n\n
One location may contain a defect while another appears nearly ideal. As a result, LIDT testing commonly evaluates damage probability across multiple sites and fluence levels rather than assuming a perfectly sharp deterministic boundary.<\/p>\n\n\n\n
The report should show or explain:<\/p>\n\n\n\n
- \n
- Number of test sites<\/li>\n\n\n\n
- Fluence steps<\/li>\n\n\n\n
- Damage events<\/li>\n\n\n\n
- Damage probability<\/li>\n\n\n\n
- Statistical model<\/li>\n\n\n\n
- Confidence level<\/li>\n\n\n\n
- Threshold definition<\/li>\n\n\n\n
- Error or uncertainty<\/li>\n<\/ul>\n\n\n\n
A supplier should not convert the highest fluence survived by one site into a guaranteed production threshold.<\/p>\n\n\n\n
LIDT Test Methods Buyers Should Recognize<\/h2>\n\n\n\n
ISO 21254-1: General Principles<\/h2>\n\n\n\n
ISO 21254-1:2025 defines the terminology and overall principles used in LIDT testing and optical-component assurance.<\/p>\n\n\n\n
ISO 21254-2: Threshold Determination<\/h2>\n\n\n\n
ISO 21254-2:2011 describes 1-on-1 and S-on-1 threshold tests for optical laser components.<\/p>\n\n\n\n
ISO 21254-3: Handling-Capability Assurance<\/h2>\n\n\n\n
ISO 21254-3:2011 specifies methods for verifying that optical surfaces can handle a defined power or energy density. The standard distinguishes assurance testing from simply determining a threshold and includes both a statistically rigorous approach and a simpler empirical test approach.<\/p>\n\n\n\n
This distinction is valuable for buyers.<\/p>\n\n\n\n
A threshold test asks:<\/p>\n\n\n\n
\n
At what level does damage probability begin or reach the defined criterion?<\/p>\n<\/blockquote>\n\n\n\n
An assurance test asks:<\/p>\n\n\n\n
\n
Can this batch or component withstand the required operating test level under the agreed conditions?<\/p>\n<\/blockquote>\n\n\n\n
For production procurement, an assurance test at a defined level may sometimes be more useful than a general catalog threshold.<\/p>\n\n\n\n
ISO\/TR 21254-4: Damage Inspection and Detection<\/h2>\n\n\n\n
ISO\/TR 21254-4:2011 describes techniques for inspecting and detecting laser-induced damage on optical surfaces and in the bulk of components.<\/p>\n\n\n\n
The detection method matters because extremely small changes may not be visible to the unaided eye.<\/p>\n\n\n\n
Possible detection methods include:<\/p>\n\n\n\n
- \n
- Visual microscopy<\/li>\n\n\n\n
- Scattered-light monitoring<\/li>\n\n\n\n
- Changes in transmitted light<\/li>\n\n\n\n
- Changes in reflected light<\/li>\n\n\n\n
- Plasma or emission detection<\/li>\n\n\n\n
- Surface imaging<\/li>\n\n\n\n
- Interferometric inspection<\/li>\n\n\n\n
- Post-test microscopy<\/li>\n<\/ul>\n\n\n\n
Two laboratories using different damage-detection criteria may report different thresholds for apparently similar optics.<\/p>\n\n\n\n
How to Compare Two Sapphire Window LIDT Values<\/h2>\n\n\n\n
Do not compare only the headline number.<\/p>\n\n\n\n
Use the following comparison checklist:<\/p>\n\n\n\n
Parameter<\/th> Supplier A<\/th> Supplier B<\/th><\/tr> Saffierori\u00ebntatie<\/td> <\/td> <\/td><\/tr> Coated or uncoated<\/td> <\/td> <\/td><\/tr> Coating design<\/td> <\/td> <\/td><\/tr> Wavelength<\/td> <\/td> <\/td><\/tr> Pulsduur<\/td> <\/td> <\/td><\/tr> Pulsenergie<\/td> <\/td> <\/td><\/tr> Herhalingsfrequentie<\/td> <\/td> <\/td><\/tr> Pulses per site<\/td> <\/td> <\/td><\/tr> Straaldiameter<\/td> <\/td> <\/td><\/tr> Balkprofiel<\/td> <\/td> <\/td><\/tr> Invalhoek<\/td> <\/td> <\/td><\/tr> Polarisatie<\/td> <\/td> <\/td><\/tr> Test method<\/td> <\/td> <\/td><\/tr> Damage-detection method<\/td> <\/td> <\/td><\/tr> Number of sites<\/td> <\/td> <\/td><\/tr> Threshold definition<\/td> <\/td> <\/td><\/tr> Test laboratory<\/td> <\/td> <\/td><\/tr> Production lot represented<\/td> <\/td> <\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n The results are reasonably comparable only when the important test parameters are similar.<\/p>\n\n\n\n
Bijvoorbeeld:<\/p>\n\n\n\n
- \n
- 5 J\/cm\u00b2 at 1064 nm and 10 ns<\/li>\n\n\n\n
- 2 J\/cm\u00b2 at 1030 nm and 500 fs<\/li>\n<\/ul>\n\n\n\n
These numbers do not show that the first optic is automatically \u201cbetter.\u201d They represent different physical regimes.<\/p>\n\n\n\n
LIDT Test Report Requirements<\/h2>\n\n\n\n
A useful LIDT report should contain the following information.<\/p>\n\n\n\n
Sample Identification<\/h3>\n\n\n\n
- \n
- Supplier<\/li>\n\n\n\n
- Customer part number<\/li>\n\n\n\n
- Supplier part number<\/li>\n\n\n\n
- Drawing revision<\/li>\n\n\n\n
- Saffierori\u00ebntatie<\/li>\n\n\n\n
- Afmetingen<\/li>\n\n\n\n
- Coating specification<\/li>\n\n\n\n
- Coatingpartij<\/li>\n\n\n\n
- Substrate lot<\/li>\n\n\n\n
- Sample quantity<\/li>\n<\/ul>\n\n\n\n
Laser Parameters<\/h3>\n\n\n\n
- \n
- Wavelength<\/li>\n\n\n\n
- Pulsduur<\/li>\n\n\n\n
- Pulsenergie<\/li>\n\n\n\n
- Herhalingsfrequentie<\/li>\n\n\n\n
- Pulse count per site<\/li>\n\n\n\n
- Straaldiameter<\/li>\n\n\n\n
- Balkprofiel<\/li>\n\n\n\n
- Invalhoek<\/li>\n\n\n\n
- Polarisatie<\/li>\n\n\n\n
- Test environment<\/li>\n<\/ul>\n\n\n\n
Test Procedure<\/h3>\n\n\n\n
- \n
- Applicable standard<\/li>\n\n\n\n
- 1-on-1 or S-on-1 method<\/li>\n\n\n\n
- Number of sites<\/li>\n\n\n\n
- Fluence levels<\/li>\n\n\n\n
- Site spacing<\/li>\n\n\n\n
- Test-surface identification<\/li>\n\n\n\n
- Damage-detection technique<\/li>\n\n\n\n
- Threshold calculation method<\/li>\n<\/ul>\n\n\n\n
Results<\/h3>\n\n\n\n
- \n
- Damage probability<\/li>\n\n\n\n
- Threshold value<\/li>\n\n\n\n
- Uncertainty<\/li>\n\n\n\n
- Confidence level when applicable<\/li>\n\n\n\n
- Damage location<\/li>\n\n\n\n
- Damage morphology<\/li>\n\n\n\n
- Test images where required<\/li>\n\n\n\n
- Pass or fail against the customer requirement<\/li>\n<\/ul>\n\n\n\n
Traceability<\/h3>\n\n\n\n
- \n
- Test date<\/li>\n\n\n\n
- Operator or laboratory<\/li>\n\n\n\n
- Equipment identification<\/li>\n\n\n\n
- Calibration status<\/li>\n\n\n\n
- Report approval<\/li>\n\n\n\n
- Connection to the production batch<\/li>\n<\/ul>\n\n\n\n
Catalog LIDT, Qualification LIDT and Batch Assurance<\/h2>\n\n\n\n
Buyers should distinguish three types of claims.<\/p>\n\n\n\n
Catalog LIDT<\/h3>\n\n\n\n
A catalog value is a general performance statement based on a representative design or previous test.<\/p>\n\n\n\n
It may be useful during initial product selection, but it may not represent:<\/p>\n\n\n\n
- \n
- The current production batch<\/li>\n\n\n\n
- A custom coating<\/li>\n\n\n\n
- A different sapphire thickness<\/li>\n\n\n\n
- A different orientation<\/li>\n\n\n\n
- A modified cleaning process<\/li>\n\n\n\n
- The customer\u2019s exact laser conditions<\/li>\n<\/ul>\n\n\n\n
Qualification LIDT<\/h3>\n\n\n\n
A qualification test is performed on samples representing a defined component design and manufacturing process.<\/p>\n\n\n\n
This is more relevant for custom high-power laser windows.<\/p>\n\n\n\n
Batch Assurance<\/h3>\n\n\n\n
A production batch may be tested at an agreed fluence or irradiance level to provide confidence that it meets the required handling capability.<\/p>\n\n\n\n
ISO 21254-3 addresses assurance of power or energy handling capability rather than threshold determination alone.<\/p>\n\n\n\n
The buyer should decide which level of evidence is necessary based on application risk and cost.<\/p>\n\n\n\n
Should Every Production Sapphire Window Be LIDT Tested?<\/h2>\n\n\n\n
Usually not.<\/p>\n\n\n\n
Destructive or threshold-seeking tests can damage the tested sample, making 100% testing impractical for finished production parts.<\/p>\n\n\n\n
Common strategies include:<\/p>\n\n\n\n
- \n
- Testing witness samples from the coating batch<\/li>\n\n\n\n
- Testing representative production samples<\/li>\n\n\n\n
- Qualification testing of the design<\/li>\n\n\n\n
- Batch assurance at a defined sub-damage level<\/li>\n\n\n\n
- Process control combined with periodic verification<\/li>\n\n\n\n
- Testing one part from a high-value lot<\/li>\n<\/ul>\n\n\n\n
A witness coupon should represent the actual production window as closely as possible in terms of:<\/p>\n\n\n\n
- \n
- Sapphire material<\/li>\n\n\n\n
- Surface preparation<\/li>\n\n\n\n
- Schoonmaken<\/li>\n\n\n\n
- Coating run<\/li>\n\n\n\n
- Coating location<\/li>\n\n\n\n
- Thermal history<\/li>\n\n\n\n
- Handling<\/li>\n<\/ul>\n\n\n\n
The supplier should explain the relationship between the witness sample and the delivered components.<\/p>\n\n\n\n
Why a Large Safety Margin Is Still Necessary<\/h2>\n\n\n\n
Operating a laser window exactly at a reported laboratory threshold is risky.<\/p>\n\n\n\n
The installed system may differ from the test setup because of:<\/p>\n\n\n\n
- \n
- Beam hot spots<\/li>\n\n\n\n
- Alignment error<\/li>\n\n\n\n
- Power drift<\/li>\n\n\n\n
- Pulse-energy variation<\/li>\n\n\n\n
- Verontreiniging<\/li>\n\n\n\n
- Aging<\/li>\n\n\n\n
- Coating variation<\/li>\n\n\n\n
- Thermal accumulation<\/li>\n\n\n\n
- Back reflections<\/li>\n\n\n\n
- Toenemende stress<\/li>\n\n\n\n
- Measurement uncertainty<\/li>\n<\/ul>\n\n\n\n
The appropriate operating margin depends on:<\/p>\n\n\n\n
- \n
- Laser stability<\/li>\n\n\n\n
- Application criticality<\/li>\n\n\n\n
- Test confidence<\/li>\n\n\n\n
- Failure consequence<\/li>\n\n\n\n
- Environmental cleanliness<\/li>\n\n\n\n
- Replacement accessibility<\/li>\n\n\n\n
- Batch consistency<\/li>\n<\/ul>\n\n\n\n
A supplier may provide test data and manufacturing recommendations, but the laser-system designer remains responsible for defining the operating margin and verifying system-level safety.<\/p>\n\n\n\n
Calculate the Actual Exposure at the Window<\/h2>\n\n\n\n
Before sending an RFQ, determine the laser exposure at the sapphire window rather than relying only on the laser source specification.<\/p>\n\n\n\n
For a pulsed system, collect:<\/p>\n\n\n\n
- \n
- Maximum pulse energy at the window<\/li>\n\n\n\n
- Minimum expected beam diameter<\/li>\n\n\n\n
- Balkprofiel<\/li>\n\n\n\n
- Pulsduur<\/li>\n\n\n\n
- Herhalingsfrequentie<\/li>\n\n\n\n
- Number of pulses<\/li>\n\n\n\n
- Invalhoek<\/li>\n\n\n\n
- Possible hot-spot factor<\/li>\n<\/ul>\n\n\n\n
The worst-case exposure may occur when:<\/p>\n\n\n\n
- \n
- Pulse energy is at its maximum<\/li>\n\n\n\n
- Beam diameter is at its minimum<\/li>\n\n\n\n
- Alignment moves the beam toward a defect or edge<\/li>\n\n\n\n
- Back-reflected energy overlaps the incident beam<\/li>\n\n\n\n
- Contamination increases local absorption<\/li>\n<\/ul>\n\n\n\n
For an oblique beam, use the actual footprint and coating conditions at the installed angle.<\/p>\n\n\n\n
LIDT Requirements for Common Laser Applications<\/h2>\n\n\n\n
High-Power Nanosecond Lasers<\/h2>\n\n\n\n
The buyer should emphasize:<\/p>\n\n\n\n
- \n
- Energy fluence<\/li>\n\n\n\n
- Pulsduur<\/li>\n\n\n\n
- Pulse repetition rate<\/li>\n\n\n\n
- S-on-1 exposure<\/li>\n\n\n\n
- Surface and coating defects<\/li>\n\n\n\n
- Beam hot spots<\/li>\n\n\n\n
- Coating batch qualification<\/li>\n<\/ul>\n\n\n\n
Picosecond and Femtosecond Lasers<\/h2>\n\n\n\n
Important considerations include:<\/p>\n\n\n\n
- \n
- Peak intensity<\/li>\n\n\n\n
- Nonlinear absorption<\/li>\n\n\n\n
- Pulsduur<\/li>\n\n\n\n
- Beam size<\/li>\n\n\n\n
- Pulse contrast<\/li>\n\n\n\n
- Repetition-rate effects<\/li>\n\n\n\n
- Dispersion<\/li>\n\n\n\n
- Birefringentie<\/li>\n\n\n\n
- Coating electric-field design<\/li>\n<\/ul>\n\n\n\n
Femtosecond damage studies of optical materials and coatings demonstrate that bulk material and coating thresholds must be evaluated separately and under precisely defined pulse conditions.<\/p>\n\n\n\n
High-Power CW Lasers<\/h2>\n\n\n\n
The RFQ should focus on:<\/p>\n\n\n\n
- \n
- Absorption<\/li>\n\n\n\n
- Thermal lensing<\/li>\n\n\n\n
- Steady-state temperature<\/li>\n\n\n\n
- Cooling<\/li>\n\n\n\n
- Toenemende stress<\/li>\n\n\n\n
- Coating loss<\/li>\n\n\n\n
- Beam dwell time<\/li>\n\n\n\n
- Environmental contamination<\/li>\n<\/ul>\n\n\n\n
A nanosecond fluence value is not sufficient for a CW design review.<\/p>\n\n\n\n
Harmonic Generation Systems<\/h2>\n\n\n\n
Systems operating at 532 nm, 355 nm or shorter wavelengths may require particular attention to:<\/p>\n\n\n\n
- \n
- Residual fundamental wavelengths<\/li>\n\n\n\n
- Multiple-wavelength coatings<\/li>\n\n\n\n
- UV contamination sensitivity<\/li>\n\n\n\n
- Coating absorption<\/li>\n\n\n\n
- Oppervlaktefouten<\/li>\n\n\n\n
- Cleaning and packaging<\/li>\n\n\n\n
- Separate LIDT values for each wavelength<\/li>\n<\/ul>\n\n\n\n
Recommended Sapphire Window LIDT RFQ Template<\/h2>\n\n\n\n
Use the following structure when contacting a supplier.<\/p>\n\n\n\n
Sapphire Window Information<\/h3>\n\n\n\n
- \n
- Onderdeelnaam:<\/li>\n\n\n\n
- Tekeningsnummer:<\/li>\n\n\n\n
- Saffierori\u00ebntatie:<\/li>\n\n\n\n
- Outside diameter:<\/li>\n\n\n\n
- Dikte:<\/li>\n\n\n\n
- Vrije opening:<\/li>\n\n\n\n
- Kwaliteit van het oppervlak:<\/li>\n\n\n\n
- Oppervlakteruwheid:<\/li>\n\n\n\n
- Flatness:<\/li>\n\n\n\n
- Parallelisme of wig:<\/li>\n\n\n\n
- Randgeometrie:<\/li>\n\n\n\n
- Coating specification:<\/li>\n<\/ul>\n\n\n\n
Laser Information<\/h3>\n\n\n\n
- \n
- Laser type:<\/li>\n\n\n\n
- Wavelength:<\/li>\n\n\n\n
- Pulse duration:<\/li>\n\n\n\n
- Pulse energy:<\/li>\n\n\n\n
- Repetition rate:<\/li>\n\n\n\n
- Pulses per site:<\/li>\n\n\n\n
- Maximum average power:<\/li>\n\n\n\n
- Beam diameter at the window:<\/li>\n\n\n\n
- Beam profile:<\/li>\n\n\n\n
- Invalhoek:<\/li>\n\n\n\n
- Polarisatie:<\/li>\n\n\n\n
- CW, pulsed or burst operation:<\/li>\n\n\n\n
- Exposure duration:<\/li>\n\n\n\n
- Expected hot spots:<\/li>\n<\/ul>\n\n\n\n
Testing Requirements<\/h3>\n\n\n\n
- \n
- LIDT test standard:<\/li>\n\n\n\n
- 1-on-1 or S-on-1:<\/li>\n\n\n\n
- Required test level:<\/li>\n\n\n\n
- Threshold or assurance test:<\/li>\n\n\n\n
- Damage-detection method:<\/li>\n\n\n\n
- Required confidence level:<\/li>\n\n\n\n
- Number of test samples:<\/li>\n\n\n\n
- Witness sample acceptable:<\/li>\n\n\n\n
- Independent laboratory required:<\/li>\n\n\n\n
- Test report required:<\/li>\n<\/ul>\n\n\n\n
Operating Environment<\/h3>\n\n\n\n
- \n
- Bedrijfstemperatuur:<\/li>\n\n\n\n
- Cooling method:<\/li>\n\n\n\n
- Vacuum or atmosphere:<\/li>\n\n\n\n
- Cleanliness level:<\/li>\n\n\n\n
- Blootstelling aan chemische stoffen:<\/li>\n\n\n\n
- Montagemethode:<\/li>\n\n\n\n
- Back-reflection risk:<\/li>\n\n\n\n
- Failure consequence:<\/li>\n<\/ul>\n\n\n\n
Commercial Information<\/h3>\n\n\n\n
- \n
- Aantal prototypes:<\/li>\n\n\n\n
- Productiehoeveelheid:<\/li>\n\n\n\n
- Annual demand:<\/li>\n\n\n\n
- Gewenste leverdatum:<\/li>\n\n\n\n
- Required certifications:<\/li>\n\n\n\n
- Lot-traceability requirement:<\/li>\n<\/ul>\n\n\n\n
Example of a Complete High-Power Laser Sapphire Window Inquiry<\/h2>\n\n\n\n
\n
Gelieve een offerte op te stellen voor op maat gemaakte saffierramen voor het C-vlak, conform de bijgevoegde tekening.<\/p>\n\n\n\n
Finished size: \u00d850 mm \u00d7 3 mm
Clear aperture: \u00d845 mm
Beide grote oppervlakken: optisch gepolijst
Coating: narrowband AR coating on both sides
Operating wavelength: 1064 nm
Laser type: pulsed Nd
Pulse duration: 10 ns
Maximum pulse energy at the window: according to attached laser specification
Repetition rate: 20 Hz
Beam diameter at the window: 8 mm using the stated beam-radius definition
Beam profile: approximately Gaussian
Angle of incidence: 0\u00b0
Polarization: linear
Required LIDT test: S-on-1 according to the agreed ISO 21254 procedure
Required documentation: complete test conditions, damage probability results, sample identification and coating-batch traceability
Quantity: 5 qualification samples and 50 production pieces<\/p>\n\n\n\nPlease state whether the LIDT result applies to the bare sapphire substrate, the coating, a witness sample or the complete finished window.<\/p>\n<\/blockquote>\n\n\n\n
This information allows the supplier and coating engineer to evaluate whether the requested performance is feasible and which qualification method is appropriate.<\/p>\n\n\n\n
Questions to Ask a Sapphire Window Supplier<\/h2>\n\n\n\n
Before approving a supplier, ask:<\/p>\n\n\n\n
- \n
- Does the quoted LIDT apply to bare or coated sapphire?<\/li>\n\n\n\n
- What wavelength and pulse duration were used?<\/li>\n\n\n\n
- Was the test 1-on-1 or S-on-1?<\/li>\n\n\n\n
- How many pulses were applied at each site?<\/li>\n\n\n\n
- What was the beam diameter and profile?<\/li>\n\n\n\n
- Was the value based on peak or average fluence?<\/li>\n\n\n\n
- How was damage detected?<\/li>\n\n\n\n
- How many test sites and samples were used?<\/li>\n\n\n\n
- What sapphire orientation was tested?<\/li>\n\n\n\n
- Was the tested coating identical to the proposed production coating?<\/li>\n\n\n\n
- Was a witness coupon or finished window tested?<\/li>\n\n\n\n
- Is the coating batch traceable?<\/li>\n\n\n\n
- Was the test performed internally or by an independent laboratory?<\/li>\n\n\n\n
- Is the result a threshold test or an assurance test?<\/li>\n\n\n\n
- What uncertainty or confidence level applies?<\/li>\n\n\n\n
- What operating safety margin is recommended?<\/li>\n\n\n\n
- Can the supplier repeat the test for the production batch?<\/li>\n\n\n\n
- Which manufacturing changes would require requalification?<\/li>\n<\/ol>\n\n\n\n
A supplier that provides only a single LIDT number without supporting conditions has not provided enough information for a high-power laser design decision.<\/p>\n\n\n\n
Common Buyer Mistakes<\/h2>\n\n\n\n
Comparing LIDT Values with Different Pulse Durations<\/h3>\n\n\n\n
A nanosecond result cannot be directly compared with a femtosecond result.<\/p>\n\n\n\n
Using Substrate Data for a Coated Window<\/h3>\n\n\n\n
The coating may determine the real damage limit of the finished component.<\/p>\n\n\n\n
Ignoring Repetition Rate<\/h3>\n\n\n\n
Single-pulse survival does not guarantee reliable repeated-pulse operation.<\/p>\n\n\n\n
Providing Beam Diameter Without Its Definition<\/h3>\n\n\n\n
Different beam-width conventions can produce different calculated fluence values.<\/p>\n\n\n\n
Using Average Laser Power for a Pulsed-Laser Review<\/h3>\n\n\n\n
Average power does not show the pulse fluence or peak intensity.<\/p>\n\n\n\n
Failing to Specify the Damage-Detection Method<\/h3>\n\n\n\n
A microscope, scatter detector and naked-eye inspection may identify different damage-onset levels.<\/p>\n\n\n\n
Assuming Catalog Data Guarantees Every Batch<\/h3>\n\n\n\n
Catalog data may represent a different coating design, substrate lot or test condition.<\/p>\n\n\n\n
Operating Too Close to the Reported Threshold<\/h3>\n\n\n\n
Contamination, hot spots, alignment variation and aging can reduce the margin in the installed system.<\/p>\n\n\n\n
Veelgestelde vragen<\/h2>\n\n\n\n
Does Sapphire Have a Higher LIDT Than Fused Silica?<\/h3>\n\n\n\n
There is no universal answer.<\/p>\n\n\n\n
The comparison depends on wavelength, pulse duration, substrate purity, surface preparation, coating, beam size and test method. Published studies may show different results under different conditions, so buyers should compare finished components tested under equivalent conditions rather than comparing generic material labels.<\/p>\n\n\n\n
Does a Thicker Sapphire Window Have a Higher LIDT?<\/h3>\n\n\n\n
Not necessarily.<\/p>\n\n\n\n
Surface- or coating-limited damage may not improve simply because the substrate is thicker. Thickness can affect thermal behavior, bulk propagation and mechanical performance, but it does not automatically raise the coating threshold.<\/p>\n\n\n\n
Does Better Scratch-Dig Always Mean Higher LIDT?<\/h3>\n\n\n\n
Better surface quality can reduce visible defect risk, but scratch-dig alone does not describe subsurface damage, contamination, coating defects or absorption.<\/p>\n\n\n\n
LIDT qualification should not be replaced by cosmetic inspection alone.<\/p>\n\n\n\n
Can an AR Coating Increase LIDT?<\/h3>\n\n\n\n
An AR coating reduces reflection and may be designed for high-power use, but its effect on LIDT depends on the material system, layer design, defect density, absorption and test conditions.<\/p>\n\n\n\n
A coating can improve system transmission while still becoming the component\u2019s lowest-damage-threshold region.<\/p>\n\n\n\n
Is the Highest Survived Fluence the LIDT?<\/h3>\n\n\n\n
Not necessarily.<\/p>\n\n\n\n
A formal result should be based on the agreed threshold definition, test method and damage probability\u2014not simply the highest level survived by one location.<\/p>\n\n\n\n
What Is the Difference Between LIDT Testing and Laser-Damage Assurance?<\/h3>\n\n\n\n
Threshold testing estimates damage onset under defined conditions.<\/p>\n\n\n\n
Assurance testing verifies that a component or batch can handle an agreed laser exposure level. ISO 21254-3 specifically addresses power- or energy-handling assurance.<\/p>\n\n\n\n
Can One Witness Sample Represent the Whole Coating Batch?<\/h3>\n\n\n\n
It can provide useful batch evidence when the witness sample accurately represents the substrate preparation, coating run and processing conditions.<\/p>\n\n\n\n
The customer should confirm the witness-sample location, coating-batch connection and inspection plan.<\/p>\n\n\n\n
Should the Customer Specify an Exact LIDT Number?<\/h3>\n\n\n\n
The customer should first calculate the worst-case system exposure and required safety margin.<\/p>\n\n\n\n
The resulting requirement should then be communicated together with all relevant laser and test parameters.<\/p>\n\n\n\n
Conclusie<\/h2>\n\n\n\n
Laser-induced damage threshold is an essential specification for sapphire windows used in high-power laser systems, but an LIDT number has no practical meaning without its test conditions.<\/p>\n\n\n\n
Buyers should always define:<\/p>\n\n\n\n
- \n
- Wavelength<\/li>\n\n\n\n
- Pulsduur<\/li>\n\n\n\n
- Pulsenergie<\/li>\n\n\n\n
- Straaldiameter<\/li>\n\n\n\n
- Balkprofiel<\/li>\n\n\n\n
- Herhalingsfrequentie<\/li>\n\n\n\n
- Pulses per site<\/li>\n\n\n\n
- Invalhoek<\/li>\n\n\n\n
- Polarisatie<\/li>\n\n\n\n
- Saffierori\u00ebntatie<\/li>\n\n\n\n
- Coating design<\/li>\n\n\n\n
- Test method<\/li>\n\n\n\n
- Damage-detection method<\/li>\n\n\n\n
- Required operating margin<\/li>\n<\/ul>\n\n\n\n
The most reliable purchasing approach is to qualify the complete finished sapphire window under conditions that closely represent the actual laser system.<\/p>\n\n\n\n
For a custom sapphire laser window review, send the drawing, wavelength, pulse duration, pulse energy, repetition rate, beam size, coating requirement and target test method. The supplier can then evaluate substrate preparation, coating design and the appropriate LIDT qualification or assurance plan.<\/p>","protected":false},"excerpt":{"rendered":"
Sapphire windows are widely considered for laser systems because they combine optical transmission with high hardness, mechanical strength, thermal stability and resistance to harsh environments. However, selecting a sapphire window for a high-power laser system requires more than checking its transmission range or specifying an anti-reflective coating. The buyer must also evaluate its laser-induced damage […]<\/p>\n","protected":false},"author":1,"featured_media":2688,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"set","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"categories":[17],"tags":[862,335,1083,1087,1086,1084,1044,158,1085],"class_list":["post-2687","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-industry-news","tag-ar-coated-sapphire","tag-high-power-laser-optics-2","tag-iso-21254","tag-laser-window-supplier","tag-laser-induced-damage-threshold","tag-optical-damage-testing","tag-precision-sapphire-optics","tag-sapphire-laser-window","tag-sapphire-window-lidt"],"_links":{"self":[{"href":"https:\/\/www.sapphire-windows.com\/nl\/wp-json\/wp\/v2\/posts\/2687","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.sapphire-windows.com\/nl\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.sapphire-windows.com\/nl\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.sapphire-windows.com\/nl\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.sapphire-windows.com\/nl\/wp-json\/wp\/v2\/comments?post=2687"}],"version-history":[{"count":1,"href":"https:\/\/www.sapphire-windows.com\/nl\/wp-json\/wp\/v2\/posts\/2687\/revisions"}],"predecessor-version":[{"id":2689,"href":"https:\/\/www.sapphire-windows.com\/nl\/wp-json\/wp\/v2\/posts\/2687\/revisions\/2689"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.sapphire-windows.com\/nl\/wp-json\/wp\/v2\/media\/2688"}],"wp:attachment":[{"href":"https:\/\/www.sapphire-windows.com\/nl\/wp-json\/wp\/v2\/media?parent=2687"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.sapphire-windows.com\/nl\/wp-json\/wp\/v2\/categories?post=2687"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.sapphire-windows.com\/nl\/wp-json\/wp\/v2\/tags?post=2687"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}